Capacitor burn-out test set



May 30, 1961 Filed April 3, 1957 G. MINCHENKO CAPACITOR BURN-OUT TEST SET j MK \ v I||||| Ill um Mill E. M//VDHEA// 2 Sheets-Sheet 1 -capacitors'toHburn-outf or `overvoltage tests.

United ,States Patent yCAPACI'IOR BURN-QUT IEST SET ,Georgelw'inchenkmsalem 'N.H., assigner to Western Electric'` Company,` Incorporated, New York, N.Y., a

corporation 'of New York Filed Apta- 3, ;1 9`57,.Ser. No. 650,487

j SfClaims. (Cl. 209-81) of vcapacitor failure when specified working voltages are Iapplied thereto. It is common practice to clear these actual and# latent defects-.by subjecting the completed This burnout --operation involves applying .a .gradually increasing test-potentialacross the capacitor so that the-current ythrough the faults willcreate sufficient heat to burn away factorily-` cleared capacitors `-from ithose that vremain defective after-aspeciliedtest period.

VIn general, when a capacitor Ato be.` tested `is connected n-the-testcircuit, the-:initial current through the vcapacitor -is limited to a safe.r value and,as defects are burned out and its .leakage-resistanceincreases, the current -is non-uniformlymeduced so .that the internal temperature rise -is -he1 d within. safe limits.

In-a preferred 4.embodiment ofthe invention, capac- -itors-are successivelyffed to a test positionforfa timed -test period, -where test potential-is applied through a device such as a non-linear electron discharge device whichregulates and'limits the current during the burnout period. As the faults are cleared, the leakage resistance of the capacitor and the potential thereacross increases -greatly-and rapidly, and the impedanceqof the device fincreasesfnon-linearly as the potential-thereover decreasesuntil aspecied test potential is-applied across the -capacitor. V'TheMnon-linear current characteristics of the regulating `device makeit vpossible to limit automatically-the I12R or v`internalheat generation inthe capacitor to `a safe-value -and thereby prevent 4damaging the capacitor Whenj'its leakage resistance undergoes a large change from a. short circuiting -value lto a-very high one.

"'IfA-thevspecied test potential is reached during the test period, -a-secondelectron discharge device controlled by r-the `iirst,-pa`sses `sufiicient current to actuate a sorting mechanism for passing or accepting the tested capacitor when it is released from the ,test position.

In afpreferred .embodiment of a fixture for such a test set, van intermittently driven drum is provided with `retention yteeth for `receiving capacitors and single feeding `them to the test station `where the terminal leads or pigtails thereof are forced under a pair of electrodes tween. vtest circuit of Fig. 3 through terminals 26. The capacr, Ice 2,986,274

across'which the test potential is applied. -The driven drum. s .-stoppedfor,` the predetermined test period while the-test-potentialvis applied to the capacitor. vIn the event ,the voltage across the capacitor builds up to the specified level during the test period, a pivotally mounted deflector member is moved vaway from its normal posiition alongside the drum 4to permit the good capacitor ,todrop'throngh 4an aperture in the bottom of the fixture when ,the-drum isymoved to `feed the next capacitor into the test station. If the voltage across the tested :capacitor -fails to.-.build 11p, the deector Vremains adjacentl thedrum and when the drum is moved, the tested fcapacitonis.deecteddnto a reject receptacle.

HThese. ande-other: features of the invention will r be :more `fully-understoodfrom the following detailed Vdescription, taken in conjunction with the accompanying .drawing, in which:

Eig. l-is a side elevational View of the test fixture .of the present invention;

Eig. 2 -is a view of the test fixture along the plane .ofline 2 2, :as seen in Fig. 1;

Fig. 3;.isa vschematic diagram of a preferred embodigmentcof a test. circuit for `the test set, and

, Fig. 4 showsa typical characteristic curve for a pen- `tode-type electronftube utilized in the test circuit.

-Referring nowto the drawing, the opposite endsxof a drum `11 'l1ave.sixA pairs of equally spaced retention .teeth i12 extending ,radially therefrom for supporting gcapacitorslS longitudinally along the drum. The drum is 4made of insulatingmaterial so that the leads of the gcapacitors 18 .-are :electrically isolated. M zydriven 'intermittently `through a gear train by a .six '.:revolutions-per-.minute :motor 13 such that itfis moved one-sixth of a revolution Vevery ten seconds. mittentmovementmay be obtained with a conventional ,Geneva movement or, as` illustrated in the drawv.ing,;by means ofthe single limited group of teeth ..15 Von asmall portionzof .the periphery of the Ycontinuously `driven gear. 14, at the output of the motor 13, -which engagel one-sixth `of the teeth of the smaller drum drive gearnl every; revolution thereof. Then for every revolu- T'he drum :.-is

This intertion` of` the motor drive shaft 17, the drum 11 is driven "one-sixthofa revolution in the direction designated-by thearrowin Fig. '2. Whenever the drum is stopped, a capacitor 18 (shown in phantom in Fig. 2) is sup- ;portedin :a test position'or station where its pigtails arein electrical contact with electrodes or test terminals 19 and 20 which :are `loosely supported from an insulat- .ing bar22 extending between uprightmembers y23.and

24 of a;protective.cage 25. VCollars 30 on the bar adrjacent oppositezsides ofthe contactors keep them prop- Verly,positionedpontile drum -for engagement with the .pigtails VInl-moving into test position, the pigtailsare dragged along the-lower surfaces of the electrodes which are `sufficiently lheavy so that-this action cleans thecontactlng parts to insure good electrical contact therebe- The electrodes are connected to the electrical itors 18 are fed to the drum vfrom a track 27 which comprises two parallel inclined members on Which-the pigtails of the capacitors :are supported. The feed ltrack `and the terminals 26 have been omitted from Fig. lffor ,purposes of ',clarity.

lThe lsorting means include a deecting member 2.8 attached toa chute 29 which, in turn, is pivotally mounted from a brace 3.2 supported by the top plate 33 of thet'ixture. In Fig. -1 only a portion of the brace is disclosed-to avoid unnecessary confusion in the drawing. In its no1'- Vmal position, .as seen inl-iig. 2, the deflectingfmember'zs Ymakes slidable contact with the drum between the retention teeth 12 thereof. Tested capacitors 18 are deflected by means of member'28 into the chute 29 to a Patented-MayfiBO, 1961 reject receptacle 34 in the event the defects are not cleared during the burn-out test. A solenoid 35 having an actuator link 36 attached to the chute 29 permits lifting the detlecting member 28 away from the drum 11, as seen in dashed lines in Fig. 2, so that cleared capacitors 18 may drop directly through an aperture 37 in the bottom of the fixture into a receptacle placed thereunder.

The schematic diagram of Fig. 3 is divided into two main portions, the burn-out test circuit portion 21 and the sorting means control circuit portion 52. In the test circuit portion 21, the capacitor test voltage, which is applied between electrodes 19 and 20, is derived from a direct current power supply 42, which is adjusted to the specified test potential for the capacitors 18 plus a small voltage drop to compensate for the drop in the associated circuitry. This voltage is applied to the capacitor under test through the plate circuit of a multielectrode electron tube such as a tetrode or the pentode 43 shown in drawing. A voltmeter 44 and a condenser 45 are connected in parallel with the electrodes 19 and 20 of the test fixture, the purpose of the capacitor 45 being to provide an initial short surge of current superimposed on the plate current of the tube to burn out short circuiting defects in the capacitor 18 when it first makes contact with the electrodes. The size of the capacitor 45 is selected to provide a larger than normal short circuiting current in the capacitor under test which it can safely withstand without overheating for the momentary discharge period. To initially set up the pentode circuit, a short circuit is placed between the electrodes 19 and 20, and the grid supply 46 is adjusted so that the tube operates in its constant current area and the plate current, owing through the capacitor 18, is at a prescribed value for burning out defects without overheating and damaging the capacitor. This current value is suliciently high to burn out normal short circuiting defects remaining in the capacitor 18 after the initial current surge due to the discharge of capacitor 45. For example, for burn-out testing of one microfarad tantalum capacitors which must withstand a test potential of at least 35 volts, this value may be two milliamperes, while the momentary surge discharge current may be several times this value as may be made available with capacitor 45 which, for this case, could be of 10 microfarads size. The test source 42 would be adjusted to a value of about 37 volts so that when the defects are burned out of the capacitor 18, and the current is substantially zero, the voltage drop across the tube 43 will be about two volts and the remaining 35 volts will be across the capacitor 18.

The operating characteristic curve for the pentode is similar to that disclosed in Fig. 4, the constant current value of which is adjusted to two milliamperes (as represented by the portion of the curve to the right of the knee). The non-linear current characteristics of the pentode-type electron tubes such as the 6SF7 make them ideally suited to control and limit the heating effects of the current during the burn-out period when the leakage resistance of the capacitor varies from a very low value to a very high one. So long as the leakage resistance is low, the current in the capacitor may be of a substantial value (i.e., 2 milliamperes) and yet the product of the current squared times the leakage resistance, the heat generating factor, will not be excessive. As the leakage resistance increases, however, the current is reduced rapidly in order to prevent overheating.

4 vented by the accompanying reduction in the eectivo plate voltage of the pentode which drives the pentode to operate below the knee of the curve (Fig. 4) in the region where the current changes rapidly with small changes in plate voltage. As a result, the capacitor under test gradually takes over substantially the entire voltage from the power supply until it reaches the specified test potential.

While the burn-out test circuit 21 utilizes a multielectrode electron tube in order to obtain the required nonlinear current response characteristics, it is possible to use other non-linear circuits and circuit element such as varistors and semiconductor diodes for this purpose. These devices must be arranged or biased so that their impedances increase non-linearly with a decreasing potential diference thereover in order that the temperature rise in the capacitors under test will remain within safe limits.

The control circuit 52 for operating the solenoid 35 includes an electron discharge device such as triode 53 having a sensitive, marginal relay 54 in its plate circuit. The grid bias supply 56 for the triode is adjusted to present a negative bias to the grid 55, when the electrodes 19 and 20 are short-circuited, of a value equal to the test voltage prescribed for the capacitors 18 plus the negative bias required to produce a plate current just suicient for the operation of relay 54. This bias voltage is applied in series with the voltage drop developed across the capacitor under test and the voltage drop across the capacitor 18 is in opposition to the bias of the source S6. Then when the voltage across the capacitor under test reaches the specified value, the triode 53 will conduct suiciently to operate relay 54 to control the operation of the sorting chute 29 and deflecting member 28. The operated contacts 57 of relay 54 close the energizing circuit for va relay 58 which controls the operation of the control solenoid 35 for the chute. The relay 54 is shunted with a large capacitor 59 to make it slow operating and thereby permit proper actuation of the solenoid 35 to allow the tested capacitor 18 to fall through the aperture 37 in the base of the fixture before the detlecting member 28 is returned by the release of the solenoid 35.

summarizing the automatic operation of the test set, the motor 13, which is energized through an energizing switch 62 from a source 63, drives the gear 14 to move the drum one-sixth of a revolution every ten seconds so that a pair of the retention teeth 12 engage the pigtails of the lowermost capacitor on the supply track 27 and move it up into friction engagement with the electrodes 19 and 20 in the test station for the test period. The test circuit, as shown in Fig. 3, is operative immediately as the condensers are moved into the test station. During the test period the defects of the capacitors are burned out and, in the event the capacitor clears sufficiently so that prescribed test potential builds up across it, as may be observed by the voltmeter 44, the solenoid 35 will be operated to lift the deecting member 28. When the gear 14 next drives the drum drive gear 16, the deflecting member 28 will be raised so that the tested capacitor 18 may drop through the aperture 37. On the other hand, in the event the test voltage failed to build up during the prescribed test period, the solenoid 35 will not operate and the tested capacitor will be deected by the member 28 into the chute 2.9 and the reject receptacle 34.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. A test set circuit for burning out short circuiting defects between the electrodes of capacitors, which comprises, a source potential having first and second sides, impedance means for providing a given constant maximum current with maximum voltage across the impedance means and a non-linearly reduced current with a reduction in voltage across the impedance means and having an input and an output, said input being connected to the first side of the source potential, a iirst test terminal serially connected to the output of the impedance means for connection to one lead of a capacitor under test, and a second test terminal for connection to the other lead of the capacitor under test, the second terminal being connected to the second side of the source potential, so that a large current is provided when the potential across the capacitor under test is relatively low and a relatively small current is provided when the potential to the capacitor under test is relatively high.

2. A test set according to claim 2 having a capacitor connected across the rst and second test terminals for providing a high disch-arge current through the capacitor under test.

3. A test set for burning out short circuiting defects between the electrodes of capacitors, which comprises, a source potential having rst and second sides, impedance means for providing a given constant maximum current with the maximum Voltage across the impedance means and a non-linearly reduced current with a reduction in voltage across the impedance means and having an input connected to the first side of the source potential and an output, a first test terminal serially connected to the output of the impedance means for connection to one lead of a capacitor under test, and a second test terminal for connection to the other lead of the capacitor under test, the second terminal being connected to the second side of the source potential so that a large current is provided when the potential across the capacitor under test is relatively low, an electron tube having a control grid means connected to the second test terminal for holding the electron tube below cut-off when the potential across the capacitor under test is relatively low and for permitting conduction through the electron tube when the potential across the capacitor under test is relatively high, and electro-mechanical means connected to the output of the electron tube for diverting the capacitor under test to one position if the electron tube is conducting and for diverting the capacitor under test to a second position .if the electron tube is not conducting.

4. A capacitor test and defect burn-out circuit, which comprises, fa source of potential having rst and second sides, the rst side being connectable to a capacitor under test, a pentode-type vacuum tube having a cathode connected to the second side of the potential source, an anode connected to one terminal of a capacitor under test, `and biased control grid means for providing a constant high current through the tubes fand the capacitor under test when the capacitor under test is internally short circuited and for providing a non-linear sharply decreasing current when the leakage resistance of the capacitor under test increases.

5. A test set for burn-out testing of capacitors which comprises first and second test terminals, means for successively delivering and electrically connecting individual ones of capacitors under test to the test terminals and for maintaining the electrical connection for a prescribed test period, a test circuit including a source of potential having -rst and second sides, the rst side being connectable to the rst test terminal, a pentode-type vacuum tube having a cathode connected to the second side of the potential source, an anode connected to the second test terminal, and biased control grid means for providing a constant current through the tube and the capacitor under test when the capacitor under test is internally short circuited and for providing a non-linear sharply decreasing current when the leakage resistance of the capacitor under test increases.

References Cited in the file of this patent UNITED STATES PATENTS 1,832,948 Schmidt Nov. 24, 1931 2,016,455 Purdy Oct. 8, 1935 2,031,840 McCarty Feb. 25, 1936 2,321,191 Elimendorf June 8, 1943 2,362,691 Gaiser Nov. 14, 1944 2,589,070 Frisbie et al Mar. 1l, 1952 2,736,862 Tooker Feb. 28, 1956 2,771,992 Artingstall et al Nov. 27, 1956 2,796,986 Rajchman et ral. June 25, 1957 

